Method of making corrugated asbestos sheeting



p 24, 1935 E. A. TQQHEY Er AL 2,015,416

METHOD OF MAKING CORRUGATED ASBESTOS SHEETING Filed Oct. 10, 1951INVENTORS E dwardfl Toolngy. BY John 6. flew-12am ATTORNEY M; sq.24,1935

PATENT OFFICE METHOD OF MAKING CORRUGATED ASBESTOS SHEETING Edward A.Toohey, Somerville, and John C. Kershaw, Dunellen, N. J.,

assignors to Johns-Manville Corporation, New York, N. Y., a corporationof NewYork Application October 10, 1931, Serial No. 568,036

6 Claims.

This invention relates to a shaped sheeting of felted fibers and themethod of making the same. The invention pertains especially to themethod of shaping, as, for example, corrugating heavy asbestos sheeting,such as millboard, by a method comprising the step of pressing thesheeting while in such condition that the surface is sufficiently dry toseparate readily from the pressing member and the interior of thesheeting is sufficiently wet to yield readily under pressure.

The making of asbestos millboard in conventional manner includesdistributing asbestos fibers, suitably a mixture of long and shortfibers with starch in the proportion of 1 to 8% of the weight of thefibers, in a large volume of water, as in a paper beater, forming a feltcontinuously on a moving belt, transferring the felt continuously to acylindrical drum, whereby a laminated felt is formed, and continuing theoperation of rolling up the felt around the drum, to the desiredthickness. During the rolling, the felt is compressed by an overridingsteel or iron roller. When the desired thickness, as for example,three-sixteenths inch is reached, the operation is interrupted, thecylinder of felted material around the drum is slitted-longitudinallyand removed from the drum. The resulting felt or millboard is thenstraightened and dried, as by air previously passed over steam pipes. Inthis manner there is formed a sheet composed of several plies of feltintegrally united, each felt comprising interlocked fibers.

When it is attempted to corrugate the product, as by passage in sheetform continuously between heavy steel rolls with surfaces adapted toshape the sheet into corrugations, in accordance with the usual practicein corrugating asbestos paper, it is found that the millboard is verydifiicult to shape into corrugations and that,if the millboard is bentto the desired shape, internal cracks or zones of weakness may develop.Moistening the surface, as with steam, does not solve the difficulty; ifsufilcient water is added to soften the interior properly, the surfacethrough which the water enters becomes soft enough to cause adherence tothe corrugating rolls, particularly when the rolls are slightly warm.Also, moistening with water does not unlock the fibers from the form inwhich they were set by the previous There have now been discovered meansof producing an asbestos millboard with an interior sufliciently wet tobe yielding and an exterior sumciently dry to separate readily from thecorrugating rolls.

In one embodiment of this invention, asbestos millboardthree-thirty-seconds inch thick was made in a conventional manner from amixture of short-fiber asbestos with 1 to 8, say 4, percent by weight ofstarch. As delivered from the millboard machine, the product contained40 to 60, usually about 50, percent water by weight. It was allowed todry at room temperature until the average water content was reduced toabout 20 to 35, suitably 25, percent. This condition of 10 dryness wasreached, in one instance, by drying for 12 hours at atmospherictemperature and humidity.

' The millboard partially dried, as in this manner, has a largerpercentage of water in the in- 15 terior than on the surface and has (1)a surface that is not sticky or adherent to corrugating rollers and (2)an interior that is relatively wet and capable of yielding, as tocorrugated shape. The material so dried is passed between heavy metalrolls, with shapes of surface adapted to produce corrugations or'corrugations and crossindentations. Rolls of the kind described in U. S.Patent No. 1,444,396 to Siegle may be used. After the shaping, theproduct is then thoroughly dried.-

The product is useful as a thermal insulator.

It has a degree of strength indicative of minimized internal weakness.It has practically no large internal cracks such as would result fromcorrugating millboard with a hard and dry center. The internal structureof the product is substantially uniformly strong, in distinction fromthe condition that would prevail if there were present a network ofcracks, formed during the corrugating of the millboard when dry in thecentral portion. Also, the product has a satisfactory surface that isfree from such pitting and/or scaling as would be produced by adherenceof a wet, sticky surface to the corrugating rolls, with consequentpulling out of patches of material.

A specimen of corrugated cross-indented asbestos millboard is shown inplan view in Fig. 1. In this example, there are three corrugations, thatis, three ridges and three depressions, to the inch. Thecross-indentations are 1.5 inches apart, from center to center.

Fig. 2 is a cross sectional view along the dotted line 2-2 of Fig. 1, inthe direction of the arrows. Fig. 3 is a perspective view of the'articleshown in Fig. 1.

In the various figures, ridges are indicated by the numeral I, troughsby 2, and cross-indentations by 3.

Many variations from the details of the illustrative example may be madewithout departing from the scope of this invention. Thus, there may besubstituted for the asbestos millboard other thick sheeting of asbestosor equivalent material, suitably of thickness less than onefourth inchand greater than that which may be corrugated satisfactorily when theinterior is relatively dry. Also, binders other than starch may be usedin the asbestossheeting, such as a modified starch, glue, or a rosinsine, although starch or a binder that is weak or yielding when wet andstiff when dry has been found to be especially desirable. Fibers otherthan asbestos may be present in the sheeting, as, for example, asubstantial proportion of wood pulp, old newspapers, cotton, hair,and/or wool. While the mineral fiber used is suitably a mixture ofasbestos fibers of relatively short length, such as mixed moderatelylong and short Canadian fibers, other asbestiform or mineral fibers maybe used, particularly in compositions that are yielding when wet andstiff or hard when dry. There may also be used, as a base material to beshaped, thick sheets or boards of wood pulp, such as may be made bycompositing and integrally uniting felts, as with a millboard machine.Pressing to other shapes than corrugations, with or withoutcross-indentations, may be made, as, for example, the formation ofrelatively deep indents.

In general, the sheeting is corrugated or otherwise shaped while theinterior is moist. In a preferred practice, the sheets are kept fresh,that is, not hard pressed to other form and not allowed to drycompletely before being submitted to the corrugating or other shaping ofthe surface to the final form.

The invention is not limited to any theory or explanation.

The action of moisture in the interior of the sheet is possibly. animportant factor.

The greater susceptibility to shaping of a relatively fresh sheet, ascompared to shaping of a sheet that has been set and then wetted, thatis, has been pressed, as to fiat form, dried thoroughly, and thenwetted, may be due in part also to the following effects: When a wetfelt of asbestos fibers is firmly pressed and dried, there follows moreor less interlocking and adherence of fibers. Thus, the ends of somefibers may curl partly around other fibers. Or, the fibers may be mashedtogether, by the firm pressing, sufficiently to give considerableinterlocking and surface adherence on drying. This stiffening effect ofadherence and/or interlocking of fibers is avoided by shaping a sheet tothe final form desired beforecomplete drying of the sheet or setting ofit in anotherform.

In pressing the thick sheet of exterior portion containing a lowerproportion of water than the interior, there are developed cracksextending into the sheet from the exterior surface thereof,

whereas the inner parts remain substantially free from cracks.

What we claim is:

l. The providing of irregularities of surface of a thick sheet ofcomposited and integrally united 5 felts by a method which includes thestep of pressing to, shape a sheet of the type described that has asmaller proportion of moisture on the surface than in the interior ofthe sheet.

2. In making a thick sheet of irregular surface including integrallyunited and felted asbestos fibers, the method which comprises forming athick sheet including asbestos fibers, water, and a binder that isrelatively stiif when dry and yielding when wet, partially drying thesheet to provide an outer surface'thereof that contains a smallerproportion of water than the interior of the sheet, subjecting thepartially dried sheet to a pressing operation to provide the desiredirregularities of surface, and drying the pressed sheet.

3. In making corrugated millboard including asbestos fibers and starchbinder, the method which comprises forming the millboard in wet form,subjecting the wet millboard to incomplete as drying to provide outersurfaces thereof containing a lower proportion of water than theinterior of the millboard, subjecting the partially dried millboard tocompression between corrugating rollers to corrugate it, and then dryingthe corrugated product.

4. In making corrugated millboard including asbestos fibers and starchhinder, the method which includes forming the millboard in wet form,subjecting the wet millboard to incomplete drying to render the outersurface thereof relatively non-adherent and to leave the interiorportion in readily yielding condition, subjecting the partially driedmillboard to shaping between corrugating rollers, and then drying theshaped product.

5. In making an asbestos sheet of irregular surface, the method whichcomprises forming a thick sheet consisting largely of felted asbestosfibers and water in the proportion of approximately 40 5'; to 60 partsby weight of water to 100 parts of the said sheet, drying the wet sheetto reduce the water content to approximately 20 to 35 parts for 100parts of the sheet, subjecting the incompletely dried sheet to pressurebetween rollers of irregular surface to impart irregularities of surfaceto the sheet, and then drying the product.

6. The method of making a sheet of the type described which comprisesforming a thick felt comprising fibers of asbestos and a binder thereforthat is yielding when wet and rigid when dry, pressing the felt toprovide irregularities of surface while the binder in the centralportion of the felt is in yielding undried condition, and then dryingthe thus shaped felt. '0

EDWARD A. TOOHEY.. JOHN C. KERSHAW.

